Electric vacuum cleaner

ABSTRACT

An electric vacuum cleaner in which a thyristor is provided to control the input to an electric motor driving a blower so as to adjust the flow of insucked air. In the cleaner, the thyristor is disposed in the path of airstream through the cleaner casing so that it can be subject to forced cooling, and means responsive to a variation in the pressure or in the airflow is provided to vary the phase corner the gate circuit of the thyristor for controlling the flow of insucked air.

United States Patent Inventors Tomoyuki Hosokawa Takarazuka-shi; Toshii Tsugeki, Takatsuki-shi; Shigeyuki Asanari, Suita-shi, Japan Appl. No. 750,046

Filed Aug. 5, 1968 Patented May 11, 1971 Assignee Matsushita Electric Industrial Co., Ltd

Osaka, Japan Priority Aug. 9, 1967, Aug. 9, 1967, Aug. 18, 1967 apan 42/69344, 42/69345 and 42171538 ELECTRIC VACUUM CLEANER 6 Claims, 13 Drawing Figs.

US. Cl 55/361,

15/319, 55/418, 55/471 Int. Cl A471 9/28 Field of Search 15/327;

[56] References Cited UNITED STATES PATENTS 3,142,857 8/1964 Fresard et a1 15/327E 3,209,228 9/ 1965 Gawron 318/341X 3,413,779 12/ 1968 Takahashi et a1. 15/327X 3,450,974 6/ 1969 Berlin 318/341X Primary Examiner-Robert W. Jenkins Attomey-Stevens, Davis, Miller & Mosher Patnted May 11, 1971 3,577,869

5 Sheets-Sheet 1 Patented May 11, 1971 3,577,869

5 Sheets-Sheet 5 ELECTRIC VACUUM CLEANER This invention relates to vacuum cleaners of the type driven by an electric motor.

Conventional electric vacuum cleaners generally comprise a main casing having an air suction port and a discharge port, a blower integral with an electric motor so as to be driven by the latter, and a dust-collecting filter disposed ahead of the blower-motor assembly and behind the suction port. In such electric vacuum cleaners, the flow of air passing through the filter is reduced as dust accumulates within the filter, and the reduction in the amount of insucked air tends to result in the state that the blower motor rotates at substantially no load, which gives rise to an increase in the revolution of the motor and a reduction in the power consumption.

In order to avoid such a trouble, a thyristor may be employed in the electric vacuum cleaner for controlling the input to the blower motor thereby increasing the supply current to the motor to increase the revolution of the motor and prevent the reduction in the power consumption. By the use of the thyristor, the electric motor can effectively be operated, and the undesirable reduction in the suction due to clogging of the fine meshes of the filter can be prevented so as to ensure satisfactory suction of dust in large amounts.

However, in the state in which the thyristor is controlling the input to the blower motor, a power loss corresponding to the product of the supply current and the voltage drop takes place within the thyristor and the power in a considerable amount is lost as heat. From the standpoint of protection of the thyristor, therefore, some means must be provided to positively dissipate the heat thus generated. In this connection, a heat-radiating member having a very large size is usually necessary when a method of natural radiation of heat from the thyristor is restored to. It is absolutely impracticable to enclose the thyristor equipped with such a large heat-radiating member within the main casing of the cleaner whose interior is substantially entirely occupied by the filter and the blowermotor assembly, and thus some suitable and small-sized means, in lieu of the large-sized heat-radiating member, must be provided in order to positively dissipate the heat generated in the thyristor.

The present invention contemplates the provision of an electric vacuum cleaner of the kind described which has improved means for radiating heat generated in the thyristor and in which means for controlling the thyristor controlling the input to the blower motor is provided so as to automatically regulate the amount of insucked air. I

More precisely, it is an object of the present invention to provide an electric vacuum cleaner which comprises a main casing defining therewithin a passage of air insucked with air, a dust-collecting filter in said main casing, a blower driven by an electric motor disposed within said main casing behind said dust-collecting filter, and a thyristor equipped with a heatradiating member for controlling the input to said motor, said thyristor being disposed in the space between said dust-collecting filter and said blower in such a relation that it is exposed to the airstream passing through said main casing, whereby said airstream can positively cool said thyristor and said heat-radiating member. By virtue of the above arrangement, the thyristor and the heat-radiating member can positively be cooled irrespective of the amount of dust collected within the filter. The heat-radiating member of such a small size which is about one-third or a quarter of the size of the heat-radiating member adapted for natural radiation of heat may be quite sufiicient for the full development of the performance of the thyristor, which can therefore be disposed within the limited small space defined between the filter and the blower'in the main casing without in any way sacrificing the size of the filter.

Another object of the present invention is to provide an electric vacuum cleaner of the above character is which the thyristor and the associated heat-radiating member are covered by a troughlike shielding casing of electrically insulating material having opposite end openings which communicate with the passage of dustentraining air within the main casing, so as to avoid adverse effects including interference to the electrical wiring due to contact between the thyristor and the filter during the withdrawal and replacement of the filter from and into the main casing.

A further object of the present invention is to provide an electric vacuum cleaner of the above character in which the thyristor and the associated heat-radiating member are covered by a troughlike shielding casing of electrically insulating material having its upstream side end closed, and at least one perforation is provided in the corresponding wall portion of the main casing so that the thyristor and the associated heat-radiating member can be cooled solely by the airstream drawn into the main casing through the perforation to flow through the troughlike shielding casing, whereby to positively avoid trouble including insulation deterioration of the thyristor and the heat-radiating member due to deposition of very fine dust particles entrained on the air having passed through the filter.

Another object of the present invention is to provide an electric vacuum cleaner of the above character in which switch means is provided to detect a variation in the airflow or negative pressure due to accumulation of dust within the filter and is operative to vary the phase of the gate circuit of the thyristor, thereby automatically controlling the supply current to the blower motor, increasing the supply current to the blower motor in spite of accumulation of'dust within the filter, preventing any reduction in the motor output and avoiding the undesirable reduction in the airflow for the satisfactory suction of dust.

These and other objects, advantages and features of the present invention will be apparent from the following detailed description of a few embodiments thereof taken in conjunction with the accompanying drawings, in which:

FIG. I is a partly vertical sectional, front elevational view of an embodiment of the electric vacuum cleaner according to the present invention;

FIG. 2 is an enlarged section taken on the line II-II in FIG. 1;

FIG. 3 is an electrical circuit diagram of the cleaner shown in FIG. 1;

FIG. 4 is a graphic illustration of the relation between the airflow and the pressure in the cleaner;

FIG. 5 is a graphic illustration of the relation between the power consumed by a thyristor and the effective current;

FIG. 6 is a partly vertical sectional, front elevational view of another embodiment according to the present invention;

FIG. 7 is an enlarged section taken on the line VII-VII in FIG. 6;

FIG. 8 is a partly vertical sectional, front elevational view of a further embodiment according to the present invention;

FIG. 9 is an electrical circuit diagram of the cleaner shown in FIG. 8',

FIG. 10 is a graphic illustration of waveforms appearing in the circuit shown in FIG. 9;

FIG. 11 is a graphic illustration of the relation between the insucked airflow and the amount of collected dust in the cleaner shown in FIG. 8;

FIG. 12 is an enlarged vertical section of part of a modification of the cleaner shown in FIG. 8; and

FIG. 13 is an electrical circuit diagram of the modification shown in FIG. 12.

Referring to FIGS. 1 and 2, an embodiment of the electric vacuum cleaner according to the present invention comprises a main casing 1 within which an electric motor 2 having an integral blower 4 is resiliently supported by a resilient member 3. A front cover 5 having an air suction port 8 therein is openably mounted to the front end opening of the main casing 1 by a hinge means 6 and is clamped to the main casing l by a latch means7. The main casing 1 has a discharge port 9 in its rear end wall. A dust-collecting filter or bag 10 is disposed within the main casing l with its resilient mouth portion 11 firmly held between the front cover 5 and the peripheral edge of the front end opening of the main casing 1. A troughlike shielding casing 12 of electrically insulating material having opposite end openings and upstanding sidewalls is detachably mounted within the space defined between the main casing 1 and the dust-collecting bag 10 as well as the blower 4. The detachable mounting of the shielding casing 12 is attained by sliding the upper end edges 13 of the upstanding sidewalls of the casing 12 into opposite guide channels 14 formed on the inner wall of the main casing 1. A thyristor 16 comprising a bidirectional three terminals thyristor is mounted on a heatradiating plate 15 which is floatingly supported within an airflow passage 19 by means of screws 18 and supports 17 extending upwardly from the inner bottom of the troughlike shielding casing 12. At least one perforation 20 having a diameter in the order of 3 millimeters is bored'through the wall of the main casing 1 at a position substantially opposite to the heat-radiating plate 15. The perforation 20 communicates with an external air admission hole (not shown) provided in a pressure type of collected dust indicator (not shown) disposed within a handle 21 fixed to the main casing l. The main casing 1 is supported on wheels 23 so that the cleaner can be moved over the surface being cleaned.

Referring to FIG. 3, a bidirectional three-terminal thyristor 24 having a second electrode 240 and a first electrode 24b is connected in series with the electric motor 2 and is further connected across opposite terminals 27 and 28 of a power supply 26 through a main switch 25 provided on the handle 21. A series connection including a variable resistor 29 and a capacitor 30 is connected across the second electrode 24a and the first electrode 24b of the bidirectional three-terminal thyristor 24. The common terminal of the variable resistor 29 and the capacitor 30 is connected through a trigger diode 31 with the gate 24c of the bidirectional three-terminal thyristor 24. A series connection including a fixed resistor 32 and a capacitor 33 is also connected across the second electrode 24a and the first electrode 24b of the bidirectional three-terminal thyristor 24 so as to protect the bidirectional three-terminal thyristor 24 from voltage surge. It will be seen that, when the main switch 25 is closed and an airflow-adjusting knob 34 mounted on the handle 21 is turned to adjust the variable resistor 29, the corresponding variation takes place in the phase of the gate circuit and a pulse is applied to the gate 24c through the trigger diode 31. As a result, a variation takes places in the conduction angle of the bidirectional three-terminal thyristor 241 and a variation occurs in the mean value of current flowing through the bidirectional three-terminal thyristor 24 thereby adjusting the input to the electric motor 2 and controlling the airflow.

In the state described above, the current flowing across the bidirectional three-terminal thyristor 24 is so large or in the order of 6 amperes and a corresponding voltage drop appears across the bidirectional three-terminal thyristor 24. In other words, a power loss represented by W=I-V, that is, the product of the current I flowing therethrough and the voltage drop V thereacross is developed as shown in FIG. and such a power loss is converted into heat. Therefore, the heat so generated must be dissipated in order to protect the bidirectional threeterminal thyristor 24 from damage. When natural radiation of heat is relied upon to deal with the situation, the heat-radiating plate must have a very large size which is unfit for mounting within a cleaner whose interior space is quite limited.

According to the present invention, a part of the airstream admitted into the cleaner from the suction port 8 and passing through the dust-collecting bag flows through the air passage 19 in the early stage of cleaning as shown by the arrow in FIG. 1. Thus the heat-radiating plate can be sufiiciently cooled at its upper and lower faces, and at the same time, the bidirectional three-terminal thyristor 24 can directly be cooled by the airstream. Since air purified by passing through the dust-collecting bag 10 is directed toward the heat-radiating plate 15 and the bidirectional three-terminal thyristor 24 for cooling, no problem arises in which the bidirectional threeterminal thyristor 24 becomes faulty due to deposition of dust thereon.

As the dust accumulates within the dust-collecting bag 10 and the airflow passing therethrough is reduced, a negative pressure develops within the main casing 1 as seen in FIG. 4, and as a result, external air is directly induced into the main casing 1 through the perforation 20 as shown by the arrow in FIG. 1 so as to cool the heat-radiating plate 15. Furthermore, the external air flowing into the main casing l in this manner is also effective to cool the electric motor 2 and can thus be utilized for preventing the burn of the electric motor 2 during its no-load operation.

It will be understood from the above description that the electric vacuum cleaner according to the present invention is provided with thyristor-cooling means which includes a heatradiating plate mounting the thyristor thereon and disposed in the passage of air through the maincasing 1 and at least one perforation bored in the wall of the main casing 1 at a position substantially opposite to the heat-radiating plate 15. By virtue of the above arrangement, the airstream insucked together with dust from the suction port of the main casing 1 can be utilized to cool the heat-radiating plate 15 until the dust accu-' mulates considerably within the dust-collecting bag 10, while when a negative pressure is developed within the main casing 1 due to substantial accumulation of the dust within the dustcollecting bag 10, the resultant pressure differential appearing across the perforation is utilized to admit external air therethrough to cool the heat-radiating plate 15. Thus, the heat-radiating plate 15 can always be positively cooled irrespective of the amount of dust accumulated within the dustcollecting bag 10. Because of the forced cooling system employed in the present invention, the heat-radiating plate 15 may have a small size which is about one-third or a quarter of the heat-radiating plate adapted for natural radiation of heat and yet can exhibit similar performance, while leads to a simplified structure of the thyristorcooling system.

Referring to FIGS. 6 and 7 is which like reference numerals are used to denote like parts appearing in FIGS. 1 and 2, there is shown another embodiment of the present invention which differs from the preceding embodiment in the structure of the troughlike shielding casing 12.

More precisely, the electric cleaner shown in FIGS. 6 and 7 comprises a troughlike shielding casing 12 of electrically insulating material which has one of its ends closed as shown so that the airstream flowing through a main casing 1 may not flow into an air passage 19 defined within the troughlike shielding casing 12. According to this embodiment, external air induced into the main casing 1 through a perforation 20 depending on a variation in the negative pressure developed within the main casing 1 passes through the air passage 19 to cool a heat-radiating plate 15 at its upper and lower faces, and at the same time, to directly cool a bidirectional three-terminal thyristor 24. Since the amount of dust accumulated within a dust-collecting bag 10 in the early stage of cleaning is quite small, the degree of vacuum within the main casing 1 will be represented by a point A in FIG. 4, and in such a state, external air flows into the air passage 19 through the perforation 20 in the wall of the main casing 1 to cool the heat-radiating plate 15. As the dust accumulates successively within the dustcollecting bag 10 until the degree of vacuum within the main casing 1 shifts from the point A to a point B where the degree of vacuum is much higher than that at the point A, an increased amount of external air is induced through the perforation 20 to further cool the heat-radiating plate 15.

It will be understood that, by virtue of the above structure in which the troughlike shielding casing 12 has one of its ends closed and is disposed substantially opposite to the perforation 20, the dust-entraining main airstream flowing through the main casing 1 can not flow into the air passage 19 defined within the troughlike shielding casing 12, and thus the bidirectional three-terminal thyristor 241 and the heat-radiating plate 15 can be protected against damage such as insulation deterioration due to deposition of dust thereon. Furthermore, the external air flowing into the main casing 1 in the above manner can be utilized to cool the electric motor 2 and is effective to prevent the burn of the electric motor 2 resulting from an abrupt temperature rise due to heavy clogging of the meshes of the dust-collecting bag and the resultant absence of any airstream passing therethrough.

Referring to FIGS. 8 to 13, a further embodiment of the present invention comprises a main casing 101 within which an electric motor 102 having an integral blower 1020 is resiliently supported by a resilient member 103. The main casing 101 has a discharge port 104 in its rear end wall. A front cover 105 having an air suction port 108 therein is openably mounted to the front end opening of the main casing 101 by a hinge means 106 and is clamped to the main casing 101 by a latch means 107. A dust-collecting bag 109 of cloth or the like is disposed within the main casing 101 with its resilient mouth portion 110 firmly held between the front cover 105 and the peripheral edge of the front end opening of the main casing 101. An airflow-sensitive switch 111 is disposed between the blower 102a and the dust-collecting bag 109, and comprises a support member 112 fixed at one end thereof to the main casing 101, a wind-receiving plate 114 pivotally mounted at an intermediate portion thereof on a member 113 extending forwardly from the support member 112, a spring 115 anchored to one end of the wind-receiving plate 114 and to a portion of the support member 112 so as to normally urge the other end of the wind-receiving plate 114 toward the dust-collecting bag 109, and stationary contact 116 and an opposite movable contact 117 are provided on the support member 112 and on the wind-receiving plate 114 adjacent to the other end thereof, respectively. While the amount of dust accumulated within the dust-collecting bag 109 is small and airflow in a large amount is passing through the dust-collecting bag 109, the wind-receiving plate 114 is urged by the wind in a direction as shown by the arrow against the force of the spring 115, but is urged in a direction opposite to the above direction by the force of the spring 115 as the dust accumulates successively within the dust-collecting bag 109 reducing the airflow passing therethrough. Thus, the movable contact 117 is brought into or released from contact with the stationary contact 116 depending on the airflow passing through the dust-collecting bag 109. The main casing 101 is provided with a handle 118 and is supported on wheels 119 so that the cleaner can be moved over the surface being cleaned. A main switch 120 and a collected dust viewing window 121 are provided on the handle 118. An airflow-adjusting knob 122 is mounted on the handle 118 and is associated with an annular indicia plate 123 marked thereon with the name of articles to be cleaned such as carpets, mats, wooden floors, clothes curtains and others. When the knob 122 is turned to a position corresponding to the name of the desired article to be cleaned marked on the indicia plate 123, the amount of air insucked by the electric vacuum cleaner can be adjusted to suit the particular article. In other words, the input to the electric motor is adjustable within a range of from about 100 watts to about 500 watts.

In FIG. 9, there is shown an electrical circuit diagram of the airflow control system in the electric vacuum cleaner of the present invention. A bidirectional three-terminal thyristor 124 having a first electrode 241, a second electrode 242 is connected in series with the electric motor 102 and is further connected across opposite terminals 251 and 252 of a power supply 125 through the main switch 120. A series connected including a variable resistor 126, which is adapted for interlocked operation with the airflow-adjusting knob 122, and a capacitor 127 is connected across the first electrode 241 and the second electrode 242 of the bidirectional three-terminal thyristor 124. The common terminal of the variable resistor 126 and the capacitor 127 is connected with the gate 243 of the bidirectional three-terminal thyristor 124 through a pulsegenerating element 128 which controls the phase angle of the gate circuit. A capacitor 129 for multiplying the input to the electric motor 102 is connected in series with the airflow-sensitive switch 111 and in parallel with the capacitor 127. The electrical parts disposed in the circuit described above are mostly accommodated within the handle 118 to provide for ease of repairs and overhauling.

It will be apparent that the setting of the variable resistor 126 may be varied to a suitable value in order to vary the time constant which is determined by the resistance of the variable resistor 126 and the capacitance of the capacitor 127 or 129 and thereby to vary the phase of the gate circuit. Meanwhile, as is commonly known, the bidirectional three-terminal thyristor 124 has such an operating characteristic that it responds to a variation in the phase of the gate circuit thereby to vary the amount of current flowing therethrough. Accordingly, a variation in the resistance of the variable resistor 126 caused by the manipulation of the airflow-adjusting knob 122 results in a variation in the phase of the gate circuit and a corresponding variation in the conduction angle of the bidirectional three-terminal thyristor 124. Consequently, the power input to the electric motor 102 is varied to vary the revolution of the motor, and the flow of air being sucked into the cleaner is varied. In other words, when the airflow-adjusting knob 122 is turned to a position corresponding to any desired one of articles to be cleaned such as a carpet, mat, wooden floor, clothing, curtain or the like, an airflow which is most suitable for the particular article to be cleaned can be obtained.

Suppose now that the airflow-adjusting knob 122 is turned to the position corresponding to the mat for which a substantial flow of air is required. This causes a suitable variation in the setting of the variable resistor 126. Then when the main switch 120 is closed, an airflow as shown by a point a in FIG. 11 will be obtained. As a floor-engaging nozzle (not shown) connected by a flexible hose (not shown) with the suction port 108 sweeps over the surface of the mat, dust entrained on the airstream is collected within the dust-collecting bag 109, while purified air alone passes through the dust-collecting bag 109 and the electric motor 102 to be discharged out of the discharge port 104. As the dust is accumulated increasingly within the dust-collecting bag 109 in this manner, the airflow passing through the dust-collecting bag 109 decreases gradually from the point 0 toward a point b as seen in FIG. 11.

In the early stage of cleaning in which the amount of dust accumulated within the dust-collecting, bag 109 is considerably small, the wind-receiving plate 114 is urged by the airstream in the direction of the arrow against the force of the spring 115, thereby keeping the movable contact 117 in contact with the stationary contact 116 to close the airflow-sensitive switch 111 and to connect the capacitor 129 with the gate circuit. The airflow-sensitive switch 111, however, is designed to be urged open by the force of the spring which overcomes the pressure imparted to the wind-receiving plate 114 by the airstream when the airflow is reduced to the point b. In such a situation, the airflow-sensitive switch 111 is opened to disconnect the capacitor 129 from the gate circuit.

Accordingly, the phase of the gate circuit is now determined by the combination of the variable resistor I26 and the capacitor 127, and as a result, the conduction angle of the bidirectional three-terminal thyristor 124, which has been limited to a hatched portion of the sine wave as shown in FIG. 10(a) in the airflow range between the points a and b in FIG. 11, is increased by an amount corresponding to a crosshatched portion as shown in FIG. 10(b), thereby increasing the current passing through the bidirectional three-ten minal thyristor 124 and increasing stepwise the input to the electric motor 102. As a result of the supply of the increased input to the motor 102, the airflow makes an abrupt rise from the point b to a point r: at which the airflow is substantially equal to that in the early stage of cleaning. The dust collection is further continued with the increased airflow until finally a point d is reached where no more suction of dust is capable.

Thus, in contrast to a conventional electric vacuum cleaner with which the dust that can be collected within the dust-collecting bag 109 amounts only to X grams as seen in FIG. 11

because the airflow is reduced along the curve a-be, the.

airflow in the electric vacuum cleaner according to the present invention follows the curve ab-c-d so that the dust in a larger amount of Y grams can be collected within the dusbcollecting bag 109. This means that more dust which is represented by the balance Z grams can be collected according to the present invention.

In FIG. 12, there is shown a modification of the airflow-sensitive switch 1 l 1 in the third embodiment of the present invention. More precisely, FIG. 12 shows a pressure switch disposed between the blower 102a and the dust-collecting bag 109. The pressure switch comprises a support member 130 fixed to the main casing 101 within the handle 118, a pressure-receiving plate 132 pivotally mounted at an intermediate portion thereof on a member 131 extending from the support member 130, a diaphragm 134 fixed at its top to one end of the pressure-receiving plate 132 and at the lower end edge of its opening to the peripheral edge of a pressure admission perforation 133 bored in the wall of the main casing 101, a coil spring 135 disposed within the diaphragm 134, and a stationary contact 136 and an opposite movable contact 137 provided on the support member 130 and on the other end of the pressurereceiving plate 132, respectively.

While the difference in pressure between the external air and the interior of the main casing 101 is considerably small as in the early stage of cleaning, the internal pressure of the main casing 101 is applied through the pressure admission perforation 133 to the interior of the diaphragm 134 to urge the associated end of the pressure-receiving plate 132 upwardly so that the movable contact 137 is brought into and kept in contact with the stationary contact 136. As dust accumulates successively within the dust-collecting bag 109 and the airflow passing therethrough is reduced, a negative pressure appears within the main casing 101, and as a result, the diaphragm 134 is urged in a direction of the arrow by the force of the coil spring 135, thereby causing downward movement of the associated end of the pressure-receiving plate 132 and moving the movable contact 137 away from the stationary contact 136. Thus, the pressure switch is operative in response to appearance of a negative pressure within the main casing 101.

In FIG. 13, there is shown an electrical circuit diagram of an embodiment of the present invention including the pressure switch shown in FIG. 12. The circuit diagram in FIG. 13 differs from that in FIG. 9 in that a unidirectional three-terminal thyristor 138 is employed in lieu of the bidirectional three-terminal thyristor 124 and is connected in parallel with a diode 139 in opposite polarity to each other, and a changeover switch 140 is provided so that the input to the electric motor 102 can be controlled stepwise. Suppose that the electric motor 102 is a SOO-watt motor. Then, the input to the electric motor 102 in a range between 100 watts and 300 watts is steplessly controlled by the unidirectional three-terminal thyristor 138, while in a range between 300 watts and 500 watts, the diode 139 and the unidirectional three-terminal thyristor 138 are both operated to control the input to the electric motor 102. The changeover switch M is so mounted within the main casing 101 that it can be actuated from outside the main casing 101. A diode 141 in FIG. 13 is provided 4 to protect the unidirectional three-terminal thyristor 138.

Although the airflow-sensitive switch or pressure switch described above is adapted to operate as soon as the airflow is reduced to the point b in FIG. 11, it is possible, in the case of an article such as clothing or curtain which bears a relatively small amount of dust, to suitably vary the operating point and to restrain the switch from operation so that the input-multiplying capacitor 129 for the electric motor 102 may not be placed in operation. Furthermore, the relative height between the points b and c in FIG. 11 can freely be varied by suitably varying the capacity of the input-multiplying capacitor 129.

It will be understood from the above description that the electric vacuum cleaner according to the present invention is provided with airflow control means which includes a thyristor and a switch for detecting a variation in the airflow or negative pressure due to accumulation of dust within the dust-collecting bag, which switch is operative by sensing a predetermined reduction in the airflow or a predetermined buildup of the negative pressure to vary the phase of the thyristor gate circuit thereby to automatically control the supply current to the electric motor. By virtue of the above arrangement, the supply current to the electric motor is increased as dust accumulates within the dust-collecting bag, thus preventing an undesirable reduction in the motor output and an undesirable reduction in the airflow through the dust-collecting bag.

We claim:

1. An electric vacuum cleaner comprising a main casing defining therewithin a passage for dust laden air drawn thereinto, a dust-collecting filter in said main casing, a blower driven by an electric motor disposed within said main casing behind said dust-collecting filter, and a thyristor equipped with a heat-radiating member for controlling the input to said motor, said thyristor being disposed in the space between said dust-collecting filter and said blower in such a relation that it is exposed to the airstream passing through said main casing, and control means for controlling the conduction angle of said thyristor to obtain the most suitable airflow for particular objects to be cleaned.

2. An electric vacuum cleaner comprising a main casing defining therewithin a passage of air insucked with dust, a dust-collecting filter in said main casing, a blower driven by an electric motor disposed within said main casing behind said dust-collecting filter, a thyristor equipped with a heatradiating member for controlling the input to said motor, said thyristor being disposed in the space between said dust-collecting filter and said blower in such a relation that it is exposed to the airstream passing through said main casing, and at least one perforation provided in the wall of said main casing and communicating with said space so as to supply cooling air into said space, and control means for controlling the conduction angle of said thyristor to obtain the most suitable airflow for particular objects to be cleaned.

3. An electric vacuum cleaner comprising a main casing defining therewithin a passage of air insucked with dust, a dust-collecting filter in said main casing, a blower driven by an electric motor disposed within said main casing behind said dust-collecting filter, a thyristor equipped with a heat-radiating member for controlling the input to said motor, said thyristor being disposed in the space between. said dust collecting and said blower, and a shielding casing covering said thyristor and defining therewithin a path of air which communicates with said passage of air through said main casing, and control means for controlling the conduction angle of said thyristor to obtain the most suitable airflow for particular objects to be cleaned.

4. An electric vacuum cleaner comprising a main casing defining therewithin a passage of air insucked with dust, a dust-collecting filter in said main casing, a blower driven by an electric motor disposed within said main casing behind said dust-collecting filter, a thyristor equipped with a heat-radiating member for controlling the input to said motor, said thyristor being disposed in the space between said dust-collecting filter and said blower, at least one perforation provided in the wall of said main casing and communicating with said space so as to supply cooling air into said space, and a shielding casing covering said thyristor and defining therewithin a path of air which communicates with said perforation and said passage of air through said main casing.

5. An electric vacuum cleaner comprising a main casing defining therewithin a passage of air insucked with dust, a dust-collecting filter in said main casing, a blower driven by an electric motor disposed within said main casing behind said dust-collecting filter, a thyristor equipped with a heat-radiating member for controlling the input to said motor, said thyristor being disposed in the space between said dust-collecting filter and said blower, and a shielding casing covering said thyristor and defining a path of air which communicates with said space solely at the end on the downstream side of said passage of air through said main casing, and control means for controlling the conduction angle of said thyristor to obtain the most suitable airflow for particular objects to be cleaned.

6. An electric vacuum cleaner comprising a main casing defining therewithin a passage of air insucked with dust, a

dust-collecting filter in said main casing, a blower driven by an electric motor disposed within said main casing behind said dust-collecting filter, a thyristor equipped with a heat-radiating member for controlling the input to said motor, said thyristor being disposed in the space between said dust-collecting filter and said blower, at least one perforation provided 

1. An electric vacuum cleaner comprising a main casing defining therewithin a passage for dust laden air drawn thereinto, a dustcollecting filter in said main casing, a blower driven by an electric motor disposed within said main casing behind said dustcollecting filter, and a thyristor equipped with a heat-radiating member for controlling the input to said motor, said thyristor being disposed in the space between said dust-collecting filter and said blower in such a relation that it is exposed to the airstream passing through said main casing, and control means for controlling the conduction angle of said thyristor to obtain the most suitable airflow for particular objects to be cleaned.
 2. An electric vacuum cleaner comprising a main casing defining therewithin a passage of air insucked with dust, a dust-collecting filter in said main casing, a blower driven by an electric motor disposed within said main casing behind said dust-collecting filter, a thyristor equipped with a heat-radiating member for controlling the input to said motor, said thyristor being disposed in the space between said dust-collecting filter and said blower in such a relation that it is exposed to the airstream passing through said main casing, and at least one perforation provided in the wall of said main casing and communicating with said space so as to supply cooling air into said space, and control means for controlling the conduction angle of said thyristor to obtain the most suitable airflow for particular objects to be cleaned.
 3. An electric vacuum cleaner comprising a main casing defining therewithin a passage of air insucked with dust, a dust-collecting filter in said main casing, a blower driven by an electric motor disposed within said main casing behind said dust-collecting filter, a thyristor equipped with a heat-radiating member for controlling the input to said motor, said thyristor being disposed in the space between said dust collecting and said blower, and a shielding casing covering said thyristor and defining therewithin a path of air which communicates with said passage of air through said main casing, and control means for controlling the conduction angle of said thyristor to obtain the most suitable airflow for particular objects to be cleaned.
 4. An electric vacuum cleaner comprising a main casing defining therewithin a passage of air insucked with dust, a dust-collecting filter in said main casing, a blower driven by an electric motor disposed within said main casing behind said dust-collecting filter, a thyristor equipped with a heat-radiating member for controlling the input to said motor, said thyristor being disposed in the space between said dust-collecting filter and said blower, at least one perforation provided in the wall of said main casing and communicating with said space so as to supply cooling air into said space, and a shielding casing covering said thyristor and defining therewithin a path of air which communicates with said perforation and said passage of air through said main casing.
 5. An electric vacuum cleaner comprising a main casing defining therewithin a passage of air insucked with dust, a dust-collecting filter in said main casing, a blower driven by an electric motor disposed within said main casing behind said dust-collecting filter, a thyristor equipped with a heat-radiating member for controlling the input to said motor, said thyristor being disposed in the space between said dust-collecting filter and said blower, and a shielding casing covering said thyristor and defining a path of air which communicates with said space solely at the end on the downstream side of said passage of air through said main casing, and control means for controlling the conduction angle of said thyristor to obtain the most suitable airflow for particular objects to be cleaned.
 6. An electric vacuum cleaner comprising a main casing defining therewithin a passage of air insucKed with dust, a dust-collecting filter in said main casing, a blower driven by an electric motor disposed within said main casing behind said dust-collecting filter, a thyristor equipped with a heat-radiating member for controlling the input to said motor, said thyristor being disposed in the space between said dust-collecting filter and said blower, at least one perforation provided in the wall of said main casing and communicating with said space so as to supply cooling air into said space, and a shielding casing covering said thyristor and defining a path of air which communicates with said perforation and with said space solely at the end on the downstream side of said passage of air through said main casing. 